The nervous system

Info on the nervous system.

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  • Created on: 10-04-11 14:38
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The nervous system
The nervous system allows the body to respond to changes in
the environment. This is a process usually coordinated by the
brain. Reflex actions are extrarapid responses to stimuli
[stimuli: things that set off a reaction in the nervous system for
example, light, heat, sound, gravity, smell, taste, or temperature. The
singular is stimulus ], and this process also involves the nervous
system, but bypasses the brain.
Receptors and effectors
Receptors are groups of specialised cells. They can detect changes in
the environment, which are called stimuli, and turn them into electrical
impulses. Receptors are often located in the sense organs, such as
the ear, eye and skin. Each organ has receptors sensitive to particular
kinds of stimulus.
sense receptors sensitive to
touch, pressure, pain and temperature
chemicals in food
chemicals in the air
sound and position of the head
The central nervous system CNS in humans consists of the brain and
spinal cord. When a receptor is stimulated, it sends a signal along the

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The brain then coordinates the
An effector is any part of the body that produces the response. Here
are some examples of effectors:
a muscle contracting to move the arm
a muscle squeezing saliva from the salivary gland
a gland releasing a hormone [hormone: chemical messengers
produced in glands and carried by the blood to specific organs in
the body ] into the blood
Neurones are nerve cells. They carry information as tiny electrical
signals.…read more

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A motor neurone
Where two neurones meet, there is a tiny gap called a synapse. Signals
cross this gap using chemicals. One neurone releases the chemical into
the gap. The chemical diffuses across the gap and makes the next
neurone transmit an electrical signal.
Reflex actions
When a receptor is stimulated, it sends a signal to the central
nervous system, where the brain coordinates the response. But
sometimes a very quick response is needed, one that does not
need the involvement of the brain.…read more

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The way the iris in our eye adjusts the size of the pupil in response to
bright or dim light is also a reflex action.
In bright light:
Radial muscles of the iris relax.
Circular muscles of the iris contract.
Less light enters the eye through the contracted pupil.
In dim light:
Radial muscles of the iris contract.
Circular muscles of the iris relax.
More light enters the eye through the dilated pupil.…read more


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